1. Field of the Invention
This invention relates to a liquid crystal display ("LCD") and method for making the LCD.
2. Description of the Prior Art
An LCD is a substantially a flat display which generally has two conducting plates up filled up by dielectric anisotropic liquid crystal the LCD displays a picture such as a letter, a number and the like by using variation of characteristics of reflecting light in accordance with variation of applied voltage.
This kind of LCD has two glass substrates facing each spacers therebetween for forming a space in a predetermined gap which is filled up by the liquid crystal, which will be described more in detail.
At each inner surface of two parallel transparent glass substrates a transparent electrode layer of indium tin oxide ("ITO") and an orientation layer determining the dielectric anisotropy of the liquid crystal are applied in order.
The transparent electrode layer of ITO has a certain distribution pattern. One of the glass substrates has a common electrode and the other has a segment electrode.
A sealant covers the peripheral area of the inner surface of one of the substrates except for an area for receiving the liquid crystal, which is then sintered to produce a liquid crystal cell.
At the inner side of the liquid crystal cell spacers are inserted for maintaining a constant cell gap between the substrates. And the cell gap is filled by the liquid crystal through an opening, then the opening is sealed by the sealant.
At an outer surface of each substrate a polarizer is adhered for effective display,
When voltage is applied to this kind of an LCD, the transparent electrode layers inside the two glass substrates form an electric field, resulting the dielectric anisotropy of the liquid crystal molecules between the substrates being twisted in the direction determined by the orientation layer and thereby refracting light from the outside. As a result, the molecules lying at the intersection point where the applied common electrode and the applied segment electrode meet permit the light to pass, so a picture is displayed.
In the case of a big LCD of the above described LCDs, for example, bigger than 8", it is necessary to minimize the thickness of the substrate, but it is difficult to maintain the cell gap.
In this conventional LCD, after the sealant and the spacers are formed on a substrate, the substrates are pressed under high temperature by a hot presser, and then the sealant and the spacers are pressed at the same time. After the pressure is released, the spacers attempt to recover their initial configuration but the sealant attempts to maintain the sintered condition.
Further, in the case of an STN (super twisted nematic) LCD, the rate of expansion of a soda lime glass, which is mostly used as a substrate is approximately twice that of thermoplastic sealant, which is the main reason for error in the cell gap.
Therefore, the cell gap in the central part is greater than that in the periphery, which makes the picture unclear.
In order to solve the above-described problem, a spacer coated with an adhesive is proposed, but the adhesive chemically reacts with dielectric anisotropic liquid crystal. Therefore, it is difficult to put it to practical use.